Internal combustion engines although highly developed, dependable and relied upon for almost all road transportation throughout the world generally lose about 72-75% of the fuel heating value through radiation, engine coolant and exhaust. The measured brake horsepower of a typical six-cylinder spark ignition automobile was only 21% of the fuel heating value at 72 MPH and only 18% at 43 MPH, Internal Combustion Engine Fundamentals, J. B. Heywood, McGraw Hill 1988 pg. 675. Meanwhile, increasing fuel prices and shortages mount steadily as world supplies dwindle and air pollution problems continue. While there have been several attempts to provide greater efficiency in an internal combustion engine by recovering energy from waste heat, prior proposals have had marked shortcomings. One prior system developed by BMW International (U.S. Pat. No. 6,834,503) requires, in addition to the internal combustion engine, an entirely separate steam expander that is connected to the internal combustion engine by a belt to recover power from engine coolant and an exhaust powered steam generator. This arrangement adds considerably to the size, weight and expense of the power plant as well as placing limitations on thermal recovery. Because of space constraints in a vehicle, the volume and weight of the complete unit is critical. Porsche AG developed a waste heat turbine that was geared to an I.C. engine (U.S. Pat. No. 4,590,766).
The present invention aims to provide a way to recycle steam continuously in a closed circuit (no steam exhaust) through a high efficiency expander where economy of operation is the prime consideration while the same time improving I.C. emissions. Attempts have been made to combine a gas and steam engine for recovering waste engine heat, examples of which are the Still engine (GB Patent 25,356 of 1910 and 28,472 of 1912 and U.S. Pat. No. 1,324,183) and Mason U.S. Pat. No. 3,921,404. Still has a cylinder cover below the piston that provides a thin annular chamber which allows steam to flow in and out between the cover and the piston from an opening in the cylinder wall. In a counterflow engine, steam pressure throughout the entire cylinder falls close to atmospheric during the entire exhaust stroke producing a drop in steam temperature which cools cylinder walls allowing condensation of the steam admitted on the next power stroke. This robs the engine of power that would otherwise be available by reducing the mean effective cylinder pressure of the incoming charge of steam. However, the efficiency of steam engines operating on what is known as the uniflow principle achieve much greater efficiency than in a counterflow steam engine by reducing the condensation of steam. The inventor of a steam-only uniflow engine described in U.S. Pat. Nos. 2,402,699 and 2,943,608 reported tests showing a thermal efficiency of 38.2% at 3450 RPM. A double acting hollow piston uniflow engine is described in Marks Standard handbook for Mechanical Engineers, 1987 Section 9-37 as the “last great improvement in design” but it is unsuited for use as a combination internal combustion and steam car engine in part due to overheating of the piston.
One object of the present invention is to provide a combined internal combustion and steam engine that overcomes thermal inefficiencies inherent in prior combination engines but has the advantage of utilizing I.C. components (piston, cylinder, connecting rod and crankshaft) and efficiency gains that result from sharing some of the I.C. mechanical losses as well as having a compact unobstructed combustion chamber without pockets or extensions as present in an F head (opposing valve) engine thereby permitting a high performance, high compression four I.C. valve hemispherical chamber construction. A more specific object is to provide a combination engine in which internal combustion and steam act on the same piston without steam condensing on the cylinder or piston walls or heads upon admission so as to eliminate condensation losses previously inherent in prior double acting combination engines. To accomplish this, the invention must provide an I.C. steam engine with protection against losses inherent in filling the clearance space or those due to chilling of steam chamber walls by low-pressure exhausted steam as good or better than in what as known as a uniflow engine. An important requirement in a double acting I.C. and steam engine is the need for a mechanism that uses the least possible added cylinder length to minimize engine size and weight. However, it is also necessary to prevent burnt I.C. gas/oil and blow-by gas from contaminating the steam and thereby reducing steam generator and condenser efficiency. The invention aims to add as little as possible to the cylinder length to accommodate steam yet not contaminate the steam with oil or combustion products. Another general objective of the present invention is to provide a power source for more efficiently utilizing waste heat that is built into the internal combustion engine itself so that a separate steam engine or expander is unnecessary, making possible better recovery of waste energy from the internal combustion engine as well as a reduction in the over-all volume of the power unit and its production cost together with improved operating flexibility so that the engine is well adapted for powering vehicles especially cars, buses, trucks, locomotives or aircraft. It is a more specific object of the present invention to obtain the outstanding efficiency advantages of a combustion piston having an adjacent steam chamber that is able to provide both an effective zero steam chamber clearance and a gain in mean cycle temperature. Another object is to make possible reliable steam admission timing while providing variable steam cutoff in an engine that derives power from steam and combustion acting upon a piston yet is flexible enough to operate efficiently with large variations in load and steam generator output. Yet another object is to more efficiently recover lost combustion heat by conductive transfer to a working fluid within the engine itself as well as a more efficient way of recovering waste heat from I.C. engine coolant and from engine exhaust gases. Another more specific object is to provide a way to capture and remove oil and blow-by gas before it can enter a steam line. Still another object is to find a way to accurately vary steam cutoff in an internal combustion-steam hybrid engine while being able to recompress residual steam to throttle pressure within a combustion piston.
These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims. Topic headings are for convenience of the reader and not intended to be in any way limiting.